Electric air to air heat pumps are 2 to 3 times (sometimes as high as 4
x) more efficient than plain electric heat strips. They gather heat
from the outside and transfer into your house. Work good down to about
20 degree F. Below that they are just slighty more efficient than the
plain electric heat strips... never less.

Geothermal maintain the 3 to 4 COP rating because they are using heat
from the ground loop. Much more expensive to put in than air to air
heat pumps. Payback only if you plan on staying in the same house
for 20 years or so. Payback can be as short as 5 - 10 years depending
on your local propane or other fuel costs. B.G.